Low-frequency Electromagnetic Waves Research Articles

THE IMPACT OF LOW-FREQUENCY MAGNETIC FIELD ON KETAN TAPE MATURATION: pH, DENSITY, AND TASTE

This study explores the novel effect of Extremely Low Frequency (ELF) electromagnetic waves on the fermentation process of sticky rice tape, a traditional Indonesian food made from glutinous rice. ELF electromagnetic waves are waves consisting of magnetic fields and electric fields that do not require intermediaries in their propagation and have frequencies ranging from 0-300 Hz. The study uses a unique experimental method that exposes 2 kg of sticky rice tape, divided into 10 control and 10 experimental samples, each weighing 100 grams and wrapped in ziplock plastic, to ELF electromagnetic waves for two days. The study uses a device that generates ELF electromagnetic waves with a certain intensity and frequency. The study measures the changes in the pH, density, and taste of the sticky rice tape samples after the exposure. The results show that the experimental group’s sticky rice tape had a higher pH, higher density, and sweeter taste than the control group’s sticky rice tape. The study proves the effect of ELF electromagnetic waves on the fermentation process of sticky rice tape and provides insights for the development of new food processing techniques. The study demonstrates the applicability and innovation of using ELF electromagnetic waves for food fermentation.

Wireless electromagnetic telemetry for metal cased wells: A novel approach with comprehensive channel analysis

Low-frequency electromagnetic telemetry has been widely adopted for downhole data acquisition in the oil and gas industry. However, its application in cased wells has been limited by the high magnetic permeability and low resistivity of the metal casing, which causes the casing to absorb most of the electromagnetic waves transmitted by the downhole transmitter, resulting in inaccurate downhole data acquisition. We propose a novel approach to address this issue by suspending a transmitter (tens of meters in length) in the casing and connecting it electrically to the metal casing through two connectors. By forming a circulation along the transmitter and the casing, low-frequency electromagnetic waves can penetrate through the casing and reach the formation for telemetry. To further enhance the signal received by the ground antenna, we conduct a comprehensive analysis of the complex downhole-to-surface communication channel. Notably, the channel, which consists of the formation, the casing, and the transmitter, is divided into a near field and a far field for separate analysis. Quantitative assessments of four crucial factors on the ground-received signal strength are also conducted, i.e., electromagnetic wave frequency and location of the excitation source in the transmitter, as well as the length and location of the transmitter in the well. An 80-meter telemetry device is designed and optimized for integration into the well test. Experimental results confirm the consistency between the theoretically analyzed and measured attenuation law of the ground-received signal, indicating the effectiveness of our wireless electromagnetic telemetry technique for cased wells.

Pemanfaatan Gelombang Elektromagnet Extremely Low Frequency (Elf) Dalam Ketahanan Pangan

Physics is considered an important subject that is taught as a subject in itself with various considerations. Physics is seen as both a process and a product, so successful physics learning requires attention to effective and efficient learning. The utilization of Extremely Low Frequency (ELF) electromagnetic waves has great potential in the field of food security. ELF waves have low-frequency characteristics that create a unique potential to influence microbial activity and nutrient availability in improving food security productivity. ELF waves can be used to increase the productivity and quality of food crops, as well as extend the shelf life of food products. Thus, the utilization of ELF waves can help in achieving sustainable food security. In an effort to improve food security, it is necessary to innovate and develop technology that can support agricultural productivity. More research is still needed to fully understand the mechanism of action of ELF waves and how best to use them in agricultural and food processing practices.

3D forward modeling and response characteristics of low-resistivity overburden of the CFS-PML absorbing boundary for ground-well transient electromagnetic method

This study used the stable and convergent Dufort-Frankel method to differentially discretize the diffusion equation of the ground-well transient electromagnetic secondary field. The absorption boundary condition of complex frequency-shifted perfectly matched layer (CFS-PML) was used for truncation so that the low-frequency electromagnetic wave can be better absorbed at the model boundary. A typical three-dimensional (3D) homogeneous half-space model was established and a low-resistivity cube model was analyzed under the half-space condition. The response patterns and drivers of the low-resistivity cube model were discussed under the influence of a low-resistivity overburden. The absorption boundary conditions of CFS-PML significantly affected the low-frequency electromagnetic waves. For a low-resistivity cube around the borehole, its response curve exhibited a single-peak, and the extreme point of the curve corresponded to the center of the low-resistivity body. When the low-resistivity cube was directly below the borehole, the response curve showed three extreme values (two high and one low), with the low corresponding to the center of the low-resistivity body. The total field response of the low-resistivity overburden was stronger than that of the uniform half-space model due to the low-resistivity shielding effect of electromagnetic waves. When the receiving-transmitting distance gradually increased, the effect of the low-resistivity overburden was gradually weakened, and the response of the low-resistivity cube was strengthened. It was affected by the ratio of the overburden resistivity to the resistivity of the low-resistivity body.

Turbulent dipolarization regions in the Earth’s magnetotail: ion fluxes and magnetic field changes

In this work, we consider the dynamics of ion fluxes and magnetic field changes in turbulent regions of magnetotail dipolarizations. The data from the Cluster-II mission (magnetic field measurements from fluxgate magnetometers and energetic charged particle observations from RAPID spectrometers) were used for the analysis. We study individual events and investigate statistically the changes of charged particle fluxes during magnetic field dipolarizations observed during 2001–2015. Received changes in the spectral index indicate that CNO+ ions undergo stronger acceleration during dipolarization than protons and helium ions. Before dipolarization front monotonic growth the ions flux is observed (the maximum of flux is observed at 1–1,5 min after the start of dipolarization) in the range of ∼ 92–374 keV for proton; in the energy range ∼ 138–235 keV for He+ and in the energy range of 414–638 keV for CNO+ ions. Flux increase before arriving dipolarization front may result from the reflection of plasma sheet ions at the dipolarization front and the result of the resonant interactions of ions with low-frequency electromagnetic waves.

Wireless communication for environmental monitoring at waste landfills using low-frequency electromagnetic waves

Wireless communication for environmental monitoring at waste landfills using low-frequency electromagnetic waves

A Multitask Network for People Counting, Motion Recognition, and Localization Using Through-Wall Radar.

Due to the outstanding penetrating detection performance of low-frequency electromagnetic waves, through-wall radar (TWR) has gained widespread applications in various fields, including public safety, counterterrorism operations, and disaster rescue. TWR is required to accomplish various tasks, such as people detection, people counting, and positioning in practical applications. However, most current research primarily focuses on one or two tasks. In this paper, we propose a multitask network that can simultaneously realize people counting, action recognition, and localization. We take the range-time-Doppler (RTD) spectra obtained from one-dimensional (1D) radar signals as datasets and convert the information related to the number, motion, and location of people into confidence matrices as labels. The convolutional layers and novel attention modules automatically extract deep features from the data and output the number, motion category, and localization results of people. We define the total loss function as the sum of individual task loss functions. Through the loss function, we transform the positioning problem into a multilabel classification problem, where a certain position in the distance confidence matrix represents a certain label. On the test set consisting of 10,032 samples from through-wall scenarios with a 24 cm thick brick wall, the accuracy of people counting can reach 96.94%, and the accuracy of motion recognition is 96.03%, with an average distance error of 0.12 m.

Analysis of Low-Frequency Communication of Hypersonic Vehicles in Thermodynamic and Chemical Non-Equilibrium State

A plasma sheath will be developed surrounding a hypersonic vehicle in flight, which can reflect, absorb, and scatter electromagnetic (EM) waves of lower frequencies than its own, resulting in a communication blackout. This paper focuses on knowing how to limit the absorption and reflection of low-frequency EM waves by plasma sheath in a thermodynamic and chemical non-equilibrium state. According to the temperature increment model, the energy of high-power microwave (HPM) irradiation is translated into the temperature increment of heavy particles in plasma. As a result of this modification process, the transmittance of low-frequency EM waves going through the plasma sheath in a certain time frame rises, potentially easing the communication blackout problem.

Acupuncture for lumbar myofascial pain syndrome: systematic review and Meta-analysis.

This study systematically reviewed the clinical efficacy of acupuncture for lumbar myofascial pain syndrome. The randomized controlled trials (RCTs) regarding acupuncture for lumbar myofascial pain syndrome were searched in PubMed, Cochrane Library, Web of Science, EMbase, Scopus, China national knowledge infrastructure (CNKI), Wanfang database, VIP database, and China biomedical literature service system (SinoMed) from database inception until August 1st, 2022. The Cochrane's risk of bias assessment tool was used to assess the risk of bias in all included studies, and Review Manager 5.3 software was used for statistical analysis of the extracted data. As a result, 12 RCTs, involving 1 087 patients with lumbar myofascial pain syndrome, were ultimately included. The Meta-analysis results showed that the visual analog scale (VAS) score of pain in the observation group was lower than those in the oral non-steroidal anti-inflammatory medication control [SMD=-1.67, 95%CI (-2.44, -0.90), Z=4.26, P<0.000 1] and other treatment control [low-frequency electrical stimulation, tuina, electromagnetic wave irradiation combined with piroxicam gel, SMD=-1.98, 95%CI (-2.48, -1.48), Z=7.74, P<0.000 01]. The pain rating index (PRI) score in the observation group was lower than those in the lidocaine injection control [MD=-2.17, 95%CI (-3.41, -0.93), Z=3.44, P=0.000 6] and other treatment control [low-frequency electrical stimulation, tuina, MD=-5.75, 95%CI (-9.97, -1.53), Z=2.67, P=0.008]. The present pain intensity (PPI) score in the observation group was lower than that in other treatment control [low-frequency electrical stimulation, tuina, MD=-1.04, 95%CI (-1.55, -0.53), Z=4.01, P<0.000 1]. In conclusion, compared with oral non-steroidal anti-inflammatory medication, low-frequency electrical stimulation, tuina, and electromagnetic wave irradiation combined with piroxicam gel, acupuncture is more effective in reducing pain in patients with lumbar myofascial pain syndrome; acupuncture also exhibites advantage over lidocaine injection in improving PRI score and showed better outcomes over tuina and low-frequency electrical stimulation in improving PRI and PPI scores.

Multi-Functional Electrospun AgNO3/PVB and Its Ag NP/PVB Nanofiber Membrane.

This study focuses on the fabrication of fiber membranes containing different concentrations of AgNO3 via the electrospinning technique. The AgNO3 present in the fibers is subsequently reduced to silver nanoparticles (Ag NPs) through UV irradiation. The resulting nanofiber film is characterized using scanning electron microscopy, X-ray diffraction, and evaluations of its anti-UV and anti-electromagnetic radiation properties. Experimental results demonstrate that increasing the AgNO3 content initially decreases and then increases the fiber diameter and fiber diameter deviation. Under UV light, the nanofibers fuse and bond, leading to an increase in the fiber diameter. AgNO3 is effectively reduced to Ag NPs after UV irradiation for more than 60 min, as confirmed by the characteristic diffraction peaks of Ag NPs in the XRD spectrum of the irradiated AgNO3/PVB fibers. The nanofiber film containing AgNO3 exhibits superior anti-UV performance compared to the film containing AgNO3-derived Ag NPs. The anti-electromagnetic radiation performances of the nanofiber films containing AgNO3 and AgNO3-derived Ag NPs are similar, but the nanofiber film containing AgNO3-derived Ag NPs exhibits higher performance at approximately 2.5 GHZ frequency. Additionally, at an AgNO3 concentration of less than 0.5 wt%, the anti-electromagnetic radiation performance is poor, and the shielding effect of the nanofiber film on medium- and low-frequency electromagnetic waves surpasses that on high-frequency waves. This study provides guidance for the preparation of polyvinyl butyral nanofibers, Ag NPs, and functional materials with anti-ultraviolet and anti-electromagnetic radiation properties.

Polymer self-assembly guided heterogeneous structure engineering towards high-performance low-frequency electromagnetic wave absorption

Magnetic-dielectric synergy is currently regarded as among the most effective approaches to achieve low-frequency electromagnetic wave absorption (EMA). However, designing and fabricating EMA materials with tunable magnetic-dielectric balance towards high-performance low-frequency EMA remains challenging. Herein, a polymer self-assembly guided heterogeneous structure engineering strategy is proposed to fabricate hierarchical magnetic-dielectric nanocomposite. Polymer assemblies not only can be employed as intermediates to encapsulate metal-organic frameworks and load metal hydroxide, but also that they play a crucial role for the in-situ formation of polycrystalline FeCo/Co composite nanoparticles. As a result, the minimum reflection loss (RLmin) can reach −59.61 dB at 5.4 GHz (4.8 mm) with a 20 wt% filler loading, while the effective absorption bandwidth (EAB, RLmin ≤ −10 dB) is 2.16 GHz, exhibiting excellent low-frequency EMA performance. Systematic investigations demonstrate that hierarchical mesoporous carbon matrix that supports FeCo/Co composite nanoparticles is beneficial for optimizing impedance matching and increasing attenuation capacity. In general, this study opens up new prospects for developing magnetic-dielectric EMA materials using a polymer self-assembly guided heterogeneous structure engineering strategy, which may receive significant attention in future research.

Thresholdless stochastic particle heating by a single wave.

Stochastic heating is a well-known mechanism through which magnetized particles may be energized by low-frequency electromagnetic waves. In its simplest version, under spatially homogeneous conditions, it is known to be operative only above a threshold in the normalized wave amplitude, which may be a demanding requisite in actual scenarios, severely restricting its range of applicability. In this paper we show, by numerical simulations supported by inspection of the particle Hamiltonian, that allowing for even a very weak spatial inhomogeneity completely removes the threshold, trading the requirement upon the wave amplitude with a requisite upon the duration of the interaction between the wave and particle. The thresholdless chaotic mechanism considered here is likely to be applicable to other inhomogeneous systems.

ELF-EM signal processing while drilling based on human-computer interaction combined algorithm

In the electromagnetic wave measurement while drilling (EM MWD), the extra low frequency electromagnetic wave (ELF-EM) below 20Hz was usually chosen as the carrier because of its transmission characteristics in the formation. However, as the drilling depth increases, the electromagnetic wave signals received on the ground gradually weaken, becoming lower than a certain signal-to-noise ratio (SNR) and making it impossible to be decoded or transmitted. The attenuation of electromagnetic wave in the formation is definitely one of the causes, but what matters more is the influence of environment noise at the well site, especially the in-band interference noise and random noise. Targeting at the out-of-band noise, the bandpass filter, which is invalid to the in-band noise, can be used to eliminate the noise out of the carrier's main band. To cope with the question, an algorithm based on the human-computer interaction detection (HCID) was proposed in this paper that improves the SNR of ELF-EM signals, with the effective transmission distance of EM MWD increased. In this paper, the validity of the proposed HCID algorithm was verified through communication processing performance simulation and field data comparison, thus providing a reference for engineers and technicians in this field. Theoretical analysis and experimental data verification show that the combined algorithm decodes effectively under the in-band interference noise of − 80dB SNR and in-band random noise of − 17dB SNR.

Magnetosonics with Landau levels in GaAs semiconductor systems

The propagation of low frequency electromagnetic magnetosonic waves in a quantum magneto electron–hole plasma is investigated. Both of the semiconductor plasma species are magnetically quantized at equilibrium. The quantization is included through recoil effect and Landau effects on applying quantum hydrodynamic model (QHD). Analytical results of quantum hydrodynamical model are then verified numerically for GaAs plasma system.

Construction of hierarchical carbon fiber Aerogel@Hollow Co9S8 polyhedron for high-performance electromagnetic wave absorption at low-frequency

The development of low-frequency electromagnetic wave absorption materials faces considerable obstacles due to intense coupling of wave impedance and electromagnetic dissipation capacity. Herein, a novel hierarchical structure composed of 3D interconnected carbon fibers aerogel loaded with hollow cobalt (Co)-sulfide polyhedrons (CFA@HCS) is designed. Typical 3D interconnected carbon fibers derived from bamboo cellulose fiber aerogel serve as a skeleton to support the Co9S8 with a hollow structure. The electromagnetic parameters of the composite are effectively modified by combining the carbon-based skeleton with the hollow Co9S8. The coupling interaction of the electromagnetic characteristics at low frequency can be significantly improved. Accordingly, the minimum reflection loss (RLmin) of CFA@HCS with 15 wt% filler loading reaches −53.6 dB at 3.36 GHz and its effective absorption bandwidth can cover almost all the S and C bands (3.04–8 GHz). In addition, the minimum reduction of the radar cross section (RCS) reaches –22.6 dB m2 when the incidence theta is −60°. This work demonstrates that low-frequency EMW absorption could be improved by constructing hierarchical composites of carbon fiber/transition metal sulfide.

Observation of Small-amplitude Electromagnetic Cyclotron Waves in the Solar Wind

Our previous studies on low-frequency electromagnetic cyclotron waves (ECWs) with amplitudes larger than 0.1 nT in the solar wind revealed that the left-handed (LH) polarized ECWs are the dominant waves, and these waves preferentially occur in plasma conditions of high proton speed (V p ), high proton temperature (T p ), low proton density (N p ). In the present study, using magnetic field and plasma data from the Wind mission between 2005 and 2015, we perform a survey of small-amplitude ECWs with amplitudes smaller than 0.1 nT. It is revealed for the first time that the small-amplitude right-handed (RH) polarized ECWs tend to frequently occur in plasmas characterized by low V p , low T p , low N p , although the small-amplitude LH ECWs still preferentially occur in plasma conditions similar to the LH ECWs with amplitudes larger than 0.1 nT. Further investigation shows that the occurrences of small-amplitude RH ECWs and long-lasting radial interplanetary magnetic field (lrIMF) share the similar preferential plasma conditions of low T p and low N p . During lrIMF events, in particular, the occurrence rates of RH and LH ECWs are comparable, with the occurrence rate of small-amplitude RH ECWs slightly larger than that of small-amplitude LH ECWs. The generation mechanism of the small-amplitude ECWs is discussed.

Finite velocity of ECG signal propagation: preliminary theory, results of a pilot experiment and consequences for medical diagnosis

A satisfactory model of the biopotentials propagating through the human body is essential for medical diagnostics, particularly for cardiovascular diseases. In our study, we develop the theory, that the propagation of biopotential of cardiac origin (ECG signal) may be treated as the propagation of low-frequency endogenous electromagnetic wave through the human body. We show that within this approach, the velocity of the ECG signal can be theoretically estimated, like for any other wave and physical medium, from the refraction index of the tissue in an appropriate frequency range. We confirm the theoretical predictions by the comparison with a direct measurement of the ECG signal propagation velocity and obtain mean velocity as low as v=1500 m/s. The results shed new light on our understanding of biopotential propagation through living tissue. This propagation depends on the frequency band of the signal and the transmittance of the tissue. This finding may improve the interpretation of the electric measurements, such as ECG and EEG when the frequency dependence of conductance and the phase shift introduced by the tissue is considered. We have shown, that the ECG propagation modifies the amplitude and phase of signal to a considerable extent. It may also improve the convergence of inverse problem in electrocardiographic imaging.

Recognition of Rebar in Ground-Penetrating Radar Data for the Second Lining of a Tunnel

Ground-penetrating radar (GPR) detects a tunnel with relatively low-frequency electromagnetic waves, which can result in poorly characterized reinforced steel bar (rebar) hyperbolas and make it challenging to recognize rebar. Thus, the rebar is located by using attenuation and reflection coefficients, and the hyperbolic feature of the rebar is reconstructed for recognition. Due to differences in the electromagnetic properties of rebar and other media in the second lining, the position of rebar in the one-dimensional time wave diagram (A-scan) is determined by using the attenuation and reflection coefficients. The rebar is recognized at the peak point in the A-scan. This peak point is in the opposite phase of the incident wave. The amplitude of these peaks is smaller than the peaks of the adjacent points. Then, these negative peak points are reconstructed on the two-dimensional scanning data (B-scan). Finally, the rebar is recognized by using the hyperbolic feature of the rebar. The method is applied in the Husa Tunnel in Yunnan Province, China. Moreover, in the mileage section YK81+506–YK81+542 of the Husa Tunnel, the hyperbolic feature of the reconstructed rebar is evident, and the rebar appears in the region of 5–7 ns in the B-scan.

In situ construction of complex spinel ferrimagnet in multi-elemental alloy for modulating natural resonance and highly efficient electromagnetic absorption

The contradiction between the demand for highly efficient low-frequency electromagnetic wave (EMW) absorption materials and the relatively poor permeability of existing absorbers has become increasingly prominent. However, the intrinsic natural resonance in magnetic material hinders the modulation and enhancement of permeability. Herein, (FeCoNiCu)xCr3−xO4 complex spinel ferrimagnets (CSFMs) are constructed in situ in multi-elemental alloy powders (MEAs) for the first time, via annealing treatment. The microstructure and composition of the CSFMs are regulated by adjusting the annealing temperature, aiming to modulate the natural resonance frequency and achieve highly efficient megahertz (MHz) electromagnetic absorption. Simultaneously, annealing treatment improves the crystal integrity, which is conducive to enhancing intergranular magnetic coupling to elevate permeability temperature stability and the Curie temperature. The minimum reflection loss value of the MEAs/CSFMs composites is less than −7 dB at 3 mm and the effective EMW absorption bandwidth maintains between 425 and 470 MHz at 5 mm from −50 to 150 °C. In addition, the MEAs/CSFMs composites also exhibit excellent oxidation resistance and corrosion resistance due to the oxide layer on the surface. This work offers a new and tunable strategy toward modulating the natural resonance frequency for efficient temperature-stable broadband EMW absorption at specific frequency bands.

ELF-EM fields in the multi-layer spherical ‘Earth-ionosphere’ model based on WKB

Abstract With a high signal-to-noise ratio and a great depth of exploration, the wireless electromagnetic method (WEM) has wide applications in the exploration of deep mineral resources and oil and gas reservoirs. Extremely low-frequency electromagnetic (ELF) waves emitted from a horizontal antenna are used to achieve synchronous acquisition for different receivers of multi-coverage information in a global region. However, previous research based on a planar model ignored the curvature of the Earth. This work focuses on the electromagnetic fields (EM fields) in the model of a spherical ‘Earth ionosphere’ to extend the coverage of WEM. By transferring the EM fields from a vertical electric dipole (VED) as well as a vertical magnetic dipole (VMD) in the multi-layered medium of the Earth, we obtain the formulae for the EM fields emitted by a horizontal electric dipole (HED) by using a reciprocity theorem. The correctness of the proposed method is verified by comparing it with the approximate analytical formula and previous work. Based on the above results, we have studied the propagation and frequency characteristics of electromagnetic fields in a spherical waveguide consisting of the ionosphere and earth. The results show that the electromagnetic fields under the spherical model produce interference effects that are different from those of the planar model. The electromagnetic response of the layered Earth was then discussed, and its potential as an electromagnetic technique for exploring the deep Earth was demonstrated.